Vacuum Chamber and High Vacuum Epoxy

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  • Horst
    Senior Member
    • May 2011
    • 291

    Vacuum Chamber and High Vacuum Epoxy

    I’m looking to hear from someone with real world experience in joining structural elements using epoxy.

    The vacuum chamber is an aluminum stock pot 12” in diameter x 11” tall. I have a 4”wide x 8” tall x 1” deep bar stock panel to be attached to the side of the pot. I have pocketed the bar stock ¾” deep, leaving ¼” wide edge all around and machined that edge to conform to the curved side of the pot (6” radius).

    The panel will support the manifold to which 2 (1”) ball valves will be attached as well as an instrument take-off port so the stresses (on the panel) should be confined to turning the valves on and off and just general handling.
    I do not want to penetrate the chamber with screws so the question I have is whether or not the epoxy will hold the panel on the chamber.

    There is a further complication in that the sides of the pot are not straight. I have begun bedding the panel to the pot by gluing sandpaper to the pot and rubbing the panel on it. This is working but the gaps I will need to fill will be inversely proportional to my patience. I’m down to a max gap of .030 - .040 with maybe 25% - 30% in contact.

    The epoxy I am using “Torr Seal” by Varian. They make no structural claims but other high vac. Epoxy makers have said their product was suitable. Vac. stuff does get pricey.

    Thanks in advance.
  • barts
    Senior Member
    • Aug 2002
    • 990

    #2
    Why not have someone TIG weld some mounting bosses inside the pot? A lot more sure than epoxy, and prob. less expensive.

    - Bart
    Bart Smaalders
    http://smaalders.net/barts

    Comment

    • beanbag
      Senior Member
      • Jul 2009
      • 1941

      #3
      buy hysol 1c instead. Or call the company (is it loctite by now?) to ask for recommendations.

      However, these very low outgassing epoxies are usually glass /ceramic filled and are thus
      "crunchy" and tend not to be as strong as the "regular" epoxies, like 2-ton, etc.

      But search on the internet where people ask about vacuum epoxies, and you may find cheap or strong alternatives.

      Also, aluminum and ball valves are NOT high vacuum. Maybe you don't have such strict requirements.

      Comment

      • Fasttrack
        Senior Member
        • Jul 2005
        • 6300

        #4
        What vacuum level do you need? As Beanbag said, ball valves aren't compatible with high vacuum. If you can put up with leaks at the ball valves, then you can probably put up with leaks from attaching the assembly. For instance, you can fasten it with screws and seal the screw holes with epoxy. It won't be high vacuum, but it will give you a reasonably good seal.

        What are you trying to do with the stock-pot vacuum chamber? I think the best solution is to TIG weld the panel onto the pot. I would weld from the inside and weld "all killer - no filler". Dipping a filler rod can cause contamination so the accepted practice in UHV welding is to forgo using filler at all. You want to weld from the inside to prevent virtual leaks plus it will be easier since you've got the 1/4" thick material backing up the thinner stock pot wall.
        Last edited by Fasttrack; 02-03-2013, 05:01 PM.

        Comment

        • mayfieldtm
          Senior Member
          • Jul 2002
          • 588

          #5
          I vote for Barts solution of Tig Welding.
          About 4 tons of air on the assembly when evacuated and I'm sure of 'at least' some flexing, flexing, flexing.
          I'm not sure what you mean by how high a Vacuum. There is a point where Aluminum is not a good choice, especially in large surface areas.
          If you have a very fast pumping system like a Turbo. That helps a lot.
          I have always preferred to use a traditional Glass Bell Jar and Base plate with all the Feed-throughs and valves and such in the Base plate.
          Sounds like you might be doing some specialized work.
          Vacuum Jars and such can be rather expensive, but, do hold their value well when the time comes sell them.

          Tom M.

          Comment

          • mayfieldtm
            Senior Member
            • Jul 2002
            • 588

            #6
            PS.

            Look see...

            Latest news coverage, email, free stock quotes, live scores and video are just the beginning. Discover more every day at Yahoo!


            Great bunch of fellas on this group.

            Tom M.

            Comment

            • Horst
              Senior Member
              • May 2011
              • 291

              #7
              Require a sort of medium vacuum - 250 militorr rising to 500 militorr in no less than 10 minutes. I don't know if I can do it given my knowledge, skill and resources. I’m going the overkill route wherever my funds permit. All ball valves and tube connections are HiVac rated (far in excess of what I need).

              My question is how strong is the aforementioned epoxy, and would I be unwise in using it as my only attachment method?

              Comment

              • beanbag
                Senior Member
                • Jul 2009
                • 1941

                #8
                Originally posted by Horst View Post

                My question is how strong is the aforementioned epoxy, and would I be unwise in using it as my only attachment method?
                you can look up the specs on hysol 1c, but my experience says that it is not even as strong as jb weld, and I have used jb weld in these low vacuum environments. Whereas by "low vacuum", I mean few millitorrs worth.

                Comment

                • Fasttrack
                  Senior Member
                  • Jul 2005
                  • 6300

                  #9
                  Originally posted by Horst View Post
                  Require a sort of medium vacuum - 250 militorr rising to 500 militorr in no less than 10 minutes. I don't know if I can do it given my knowledge, skill and resources.
                  Easy-peasy-lemon-squeezy. You can do it!

                  I would avoid using the epoxy as your only method to attach the plate. It might hold for awhile, but it will come loose eventually. What are you using to pump the system? That will put a limit on how much leakage you can tolerate.


                  Is this, perchance, what you are building:

                  Comment

                  • lakeside53
                    Senior Member
                    • Nov 2007
                    • 10511

                    #10
                    If you do use epoxy, it's all about very accurate measuring and mixing of the epoxy (no "eyeball measures"... either weigh the parts or extrude from a hypodermic etc), and surface prep. Here's the surface prep info I got from a friend of mine that is a expert in this field.


                    Here's the formula and instructions I promised you:

                    Formula:
                    250ml D.I. water ( H2O)
                    92.5g Sulfuric Acid ( H2SO4 )
                    35.7g Ferric Sulfate Fe2( SO4)3

                    Mixing:
                    Do this with full protective gear; Goggles, face shield, rubber gloves, rubber smock. Have a second person nearby with a hose.

                    Start with a large metal bowl of tap water with lots of ice cubes in it.
                    Weigh the tare weights of a large glass beaker labeled A and a medium glass beaker labeled B.
                    Weigh the Sulfuric acid into A and the Ferric Sulfate into B
                    Measure the D.I. water into a large glass flask and put it into the ice bath, swirling several minutes to chill the water near freezing.

                    Slowly add the sulfuric acid from A to the flask of water, a little at a time, continuing to swirl to keep the temperature from rising much. There's a lot of heat released when sulfuric acid dissolves in water, and it can cause dangerous spatters if it boils locally. When done, keep swirling until the flask is no more than slightly warm to the touch. Always add the acid to the water, never the water to the acid!

                    Add Ferric sulfate from B slowly to the mixture a little at a time, mixing well between additions.

                    Store in a sealed, acid-proof container in a safe place until use.

                    Etching procedure:
                    Heat etching solution to 150F +- 5F.
                    Clean parts with hot soapy water or degreaser until pristine and fully wettable, and rinse with DI water.
                    Etch for 11 minutes +- 1 minute.
                    Rinse immediately with copious DI water.
                    Dry at 150F for 30 minutes.

                    The spent solution is safe to dilute and wash down the drain with copious tap water.

                    This process leaves a microscopically deeply pitted surface finish on the aluminum. The pits have a high aspect ratio and a good oxide film on them, so they wet well and provide a strong chemical and mechanical bond to epoxy. The bond strength results are limited by the strength of the base epoxy.

                    Enjoy,
                    Last edited by lakeside53; 02-04-2013, 12:21 AM.

                    Comment

                    • darryl
                      Senior Member
                      • Jan 2003
                      • 14400

                      #11
                      I have no experience with high vacuums, but I do have my own 'stock pot' vacuum chamber and home made pump. I made it for degassing mixtures, urethane rubber being one. I've played around with 3M 5200, which is a one-part urethane, curing by moisture absorption, and apparently almost impossible to remove except by mechanical means. Offhand it would seem like a very good solution to a holding problem, and because it doesn't cure by evaporation of a solvent it should be good in a vacuum environment. Just .02 worth-
                      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                      Comment

                      • macona
                        Senior Member
                        • Aug 2006
                        • 9425

                        #12
                        I just got some Hysol 1C from LDS Vacuum a couple weeks ago for a project. They sell it as a torr seal alternative. It is actually the exact same thing, Varian just relabels the 1C.

                        250 to 500 mtorr is nothing. Just get a couple PVC bulkhead fittings and put those in the pot, they will easily go down to that pressure. Outgassing will not be an issue.

                        My vacuum system used to have a ball valve for venting and it would go down to 10^-6 to -7 with no problems. Never had a leak from the valve. This was not your generic home depot ball valve, this was one of the bolt together types. Though I wouldn't use them for anything other than venting on a high vacuum system since they hold a pocket of gas when closed. But for your system they will be just fine, even the cheap ones.

                        Comment

                        • darryl
                          Senior Member
                          • Jan 2003
                          • 14400

                          #13
                          Just a question on measuring the vacuum- seems to me that a gauge would give you a pretty good indication up to maybe 98 or 99% vacuum, but in that last couple percent there's a wide range in usefulness. What kind of indicator is used here?
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                          Comment

                          • Mike Burch
                            Senior Member
                            • Sep 2008
                            • 1044

                            #14
                            One trick when epoxying aluminium is to rub the contact areas of both parts with wet-and-dry sandpaper, using the epoxy as the wetting agent. This cuts through the oxide layer and gets the glue in direct contact with the parent metal.
                            (It's a good trick for painting/priming aluminium, too.)
                            No warranties with this one - I have exactly zero experience of high or any other vacuums!

                            Comment

                            • darryl
                              Senior Member
                              • Jan 2003
                              • 14400

                              #15
                              The last epoxy bonding of aluminum that I did I used the wet sand method. The final step was to gently wipe away the sanding product, then immediately replace it with fresh epoxy. At the time I was impressed with the strength of the bond. I'm sure there are dedicated bonding materials these days that don't reguire much pre-prep- these would be in use in building aircraft. I've watched some of the videos, and the workers are simply calking the joins with this 'stuff', then going about the rivetting, etc. I'll have to watch again- maybe I can catch a glimpse of the actual tubes they're using. Probably some 3M product, but maybe a Loctite product. Maybe there's a PL product that would come close to equalling the 'real thing'.
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                              Comment

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